Lubricant oil composition and method for manufacturing same

ABSTRACT

To provide a lubricating oil composition that has good detergency irrespective of the small sulfated ash content thereof, and has a good friction reducing capability even after the deterioration thereof. The lubricating oil composition contains a base oil (A), a non-metal-containing sulfur antioxidant (B), and a hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule, and has a content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom of 800 ppm by mass or more based on the total amount of the lubricating oil composition, a content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition, a sulfated ash content of 0.70% by mass or less, and a total base number of 4.0 mgKOH/g or more.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition and a method for producing the same.

BACKGROUND ART

In recent years, an engine equipped with a forced-induction mechanism is being frequently used for enhancing the output power of the engine.

In an engine equipped with a forced-induction mechanism, a lubricating oil composition is liable to deteriorate due to the high thermal load applied to the lubricating oil composition. A deteriorated lubricating oil composition is insufficient in detergency, and therefore it is necessary to blend a metal-based detergent therewith to retain the detergency and the total base number.

However, a sulfated ash content formed from the metal-based detergent or the like may be a factor of deposits in the deterioration of the lubricating oil composition. The deposits thus formed may be a factor wearing the engine components.

A lubricating oil composition having a high fuel efficiency is being demanded from the standpoint of the environmental regulation in recent years. Accordingly, the lubricating oil composition is demanded to retain the friction reducing capability even after the deterioration thereof.

The techniques described in PTLs 1 and 2 have been proposed for the inhibition of deterioration of a lubricating oil composition.

CITATION LIST Patent Literatures

-   -   PTL 1: Japanese Patent No. 5,710,501     -   PTL 2: Japanese Patent No. 5,930,904

SUMMARY OF INVENTION Technical Problem

PTL 1 describes a lubricating oil composition containing at least 90% by weight of a base oil and a particular antioxidant, such as a sulfurized fatty acid.

PTL 2 describes a lubricating oil composition containing a base oil, a particular hindered amine compound, and an organic molybdenum compound.

The lubricating oil composition of PTL 1 is suppressed in the deterioration of the lubricating oil composition due to oxidation. The lubricating oil composition of PTL 2 is suppressed in the deterioration of the lubricating oil composition due to NOR.

However, the lubricating oil compositions of PTLs 1 and 2 do not consider the retention of the friction reducing capability after the deterioration of the lubricating oil composition.

The present invention has been made in view of the aforementioned circumstances, and an object thereof is to provide a lubricating oil composition that has good detergency irrespective of the small sulfated ash content thereof, and has a good friction reducing capability even after the deterioration thereof, and a method for producing the same.

Solution to Problem

The present invention provides the following items [1] and [2].

-   -   [1] A lubricating oil composition, containing a base oil (A), a         non-metal-containing sulfur antioxidant (B), and a hindered         amine antioxidant (C) having one piperidine-derived skeleton in         a molecule, and having a content of the non-metal-containing         sulfur antioxidant (B) as converted in terms of sulfur atom of         800 ppm by mass or more based on the total amount of the         lubricating oil composition, a content of the hindered amine         antioxidant (C) as converted in terms of nitrogen atom of 100         ppm by mass or more and 400 ppm by mass or less based on the         total amount of the lubricating oil composition, a sulfated ash         content of 0.70% by mass or less, and a total base number of 4.0         mgKOH/g or more.     -   [2] A method for producing a lubricating oil composition,         including preparing a lubricating oil composition containing a         base oil (A), a non-metal-containing sulfur antioxidant (B), and         a hindered amine antioxidant (C) having one piperidine-derived         skeleton in a molecule, the preparing step being performed to         satisfy the following conditions (i) to (iv):     -   (i) the lubricating oil composition having a content of the         non-metal-containing sulfur antioxidant (B) as converted in         terms of sulfur atom of 800 ppm by mass or more based on the         total amount of the lubricating oil composition,     -   (ii) the lubricating oil composition having a content of the         hindered amine antioxidant (C) as converted in terms of nitrogen         atom of 100 ppm by mass or more and 400 ppm by mass or less         based on the total amount of the lubricating oil composition,     -   (iii) the lubricating oil composition having a sulfated ash         content of 0.70% by mass or less, and     -   (iv) the lubricating oil composition having a total base number         of 4.0 mgKOH/g or more.

Advantageous Effects of Invention

The lubricating oil composition of the present invention has good detergency irrespective of the small sulfated ash content thereof, and has a good friction reducing capability even after the deterioration thereof. The method for producing a lubricating oil composition of the present invention can readily produce a lubricating oil composition that exhibits the aforementioned effects.

DESCRIPTION OF EMBODIMENTS [Lubricating Oil Composition]

The lubricating oil composition of the present embodiment contains a base oil (A), a non-metal-containing sulfur antioxidant (B), and a hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule, and has a content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom of 800 ppm by mass or more based on the total amount of the lubricating oil composition, a content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition, a sulfated ash content of 0.70% by mass or less, and a total base number of 4.0 mgKOH/g or more.

<Base Oil (A)>

The base oil (A) may be a mineral oil or a synthetic oil, and a mixed oil of a mineral oil and a synthetic oil may also be used.

Examples of the mineral oil include an atmospheric residual oil obtained by distilling a crude oil, such as a paraffin mineral oil, an intermediate base mineral oil, and a naphthene mineral oil, under an atmospheric pressure; a distilled oil obtained by distilling the atmospheric residual oil under reduced pressure; a mineral oil obtained by subjecting the distilled oil to one or more of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, and the like; and a mineral oil obtained by isomerizing wax produced by the Fischer-Tropsch process or the like (GTL wax (gas-to-liquid wax)). The mineral oil is preferably a mineral oil that is classified to Group 3 in the base oil classification by American Petroleum Institute.

Examples of the synthetic oil include a hydrocarbon synthetic oil and an ether synthetic oil. Examples of the hydrocarbon synthetic oil include an α-olefin oligomer, such as polybutene, polyisobutylene, a 1-octene oligomer, a 1-decene oligomer, and an ethylene-propylene copolymer, or a hydrogenated product thereof, an alkylbenzene, and an alkylnaphthalene. Examples of the ether synthetic oil include polyoxyalkylene glycol and polyphenyl ether.

The base oil may be a single system using any one kind of the mineral oils and the synthetic oils described above, and may be a mixed system, such as a mixture of two or more kinds of the mineral oil, a mixture of two or more kinds of the synthetic oil, and a mixture of one kind or two or more kinds of each of the mineral oil and the synthetic oil.

The base oil (A) preferably has a kinematic viscosity at 100° C. of from 2.0 to 20.0 mm²/s, more preferably from 2.0 to 15.0 mm²/s, further preferably from 2.0 to 7.0 mm²/s, and still further preferably from 2.0 to 5.0 mm²/s.

The kinematic viscosity at 100° C. of the base oil (A) that is 2.0 mm²/s or more is preferred since the evaporation loss may be small. The kinematic viscosity at 100° C. of the base oil (A) that is 20.0 mm²/s or less is preferred since the power loss due to the viscosity resistance can be suppressed to achieve improvement in fuel efficiency.

The base oil (A) preferably has a viscosity index of 80 or more, more preferably 100 or more, and further preferably 120 or more, from the standpoint of the suppression of the viscosity change by the temperature change, and the enhancement of the fuel efficiency.

In the case where the base oil (A) is a mixed oil of two or more kinds selected from a mineral oil and a synthetic oil, the mixed oil preferably has a kinematic viscosity and a viscosity index within the aforementioned ranges.

In the description herein, the “kinematic viscosity at 100° C.” and the “viscosity index” are values that are measured and calculated according to JIS K2283:2000.

The content of the base oil (A) is preferably less than 90% by mass based on the total amount (100% by mass) of the lubricating oil composition. With the content of the base oil (A) of less than 90% by mass, the amounts of the non-metal-containing sulfur antioxidant (B) and the hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule described later can be ensured to facilitate the achievement of the effects of the present invention.

The content of the base oil (A) is more preferably 60% by mass or more and less than 90% by mass, further preferably 70% by mass or more and 85% by mass or less, and still further preferably 75% by mass or more and 85% by mass or less, based on the total amount of the lubricating oil composition.

<Non-Metal-Containing Sulfur Antioxidant (B)>

The non-metal-containing sulfur antioxidant (B) is a compound that contains at least one sulfur atom and does not contain a metal atom. The lubricating oil composition of the present embodiment has a content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom of 800 ppm by mass or more based on the total amount of the lubricating oil composition.

In the case where the lubricating oil composition does not contain the non-metal-containing sulfur antioxidant (B), or in the case where the lubricating oil composition contains the non-metal-containing sulfur antioxidant (B), but the content thereof as converted in terms of sulfur atom is less than 800 ppm by mass based on the total amount of the lubricating oil composition, the friction reducing effect after the deterioration of the lubricating oil composition cannot be retained.

In the description herein, the content of sulfur atom is a value that is measured according to ASTM D-1552.

The prevention of the content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom from becoming excessive facilitates the suppression of the viscosity increase in the thermal deterioration of the lubricating oil composition. Accordingly, from the standpoint of the retention of the friction reducing effect and the suppression of the viscosity increase after the deterioration of the lubricating oil composition, the content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom is preferably 800 ppm or more and 6,500 ppm by mass or less, more preferably 1,000 ppm or more and 6,500 ppm by mass or less, and further preferably 1,500 ppm or more and 6,200 ppm by mass or less, based on the total amount of the lubricating oil composition.

Examples of the non-metal-containing sulfur antioxidant (B) include one or more kind selected from a thiocarbamate compound, a thiadiazole compound, a polysulfide compound, and a sulfurized fat or fatty oil. Among these, one or more kind selected from a thiocarbamate compound, a thiadiazole compound, and a polysulfide compound is preferred from the standpoint of the suppression of the viscosity increase after deterioration of the lubricating oil composition.

Examples of the thiocarbamate compound include compounds represented by the following general formulae (1A) and (1B).

In the formula (1A), R¹ to R⁴ each represent an alkyl group having from 1 to 30 carbon atoms or a phenyl group, in which R¹ to R⁴ may be the same as or different from each other; and R⁵ represents an alkylene group having from 1 to 10 carbon atoms.

In the formula (1B), R⁶ and R⁷ each represent an alkyl group having from 1 to 30 carbon atoms or a phenyl group, in which R⁶ and R⁷ may be the same as or different from each other; and R⁸ represents a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms.

In the formula (1A), R¹ to R⁴ each preferably represent an alkyl group having from 1 to 12 carbon atoms or a phenyl group, more preferably represent an alkyl group having from 2 to 8 carbon atoms or a phenyl group, and further preferably represent an alkyl group having from 3 to 5 carbon atoms. R¹ to R⁴ are preferably the same as each other.

In the formula (1A), R⁵ preferably represents an alkylene group having 1 or 2 carbon atoms, and more preferably an alkylene group having 2 carbon atoms (i.e., an ethylene group).

In the formula (1B), R⁶ and R⁷ each preferably represent an alkyl group having from 1 to 12 carbon atoms or a phenyl group, more preferably represent an alkyl group having from 2 to 8 carbon atoms or a phenyl group, and further preferably represent an alkyl group having from 3 to 5 carbon atoms. R⁶ and R⁷ are preferably the same as each other.

In the formula (1B), R⁸ preferably represents an alkylene group having 1 or 2 carbon atoms, and more preferably an alkylene group having 2 carbon atoms (i.e., an ethylene group).

Specific examples of the thiocarbamate compound represented by the formula (1A) include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylene bis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), and ethylene bis(dihexyldithiocarbamate).

Specific examples of the thiocarbamate compound represented by the formula (1B) include diethylthiocarbamic acid, methylene diethylthiocarbamate, ethylene diethyldithiocarbamate, dipropylthiocarbamic acid, methylene dipropylthiocarbamate, ethylene dipropyldithiocarbamate, dibutyldithiocarbamic acid, methylene dibutyldithiocarbamate, ethylene dibutyldithiocarbamate, dipentyldithiocarbamic acid, methylene dipentyldithiocarbamate, ethylene dipentyldithiocarbamate, methylene dihexyldithiocarbamate, and ethylene dihexyldithiocarbamate.

Examples of the thiadiazole compound include a compound having a 1,3,4-thiadiazole or 1,2,4-thiadiazole as a skeleton in a molecule.

Specific examples of the thiadiazole compound include 2,5-bis(n-hexyldithio)-1,3,4-thiadiazole, 2,5-bis(n-octyldithio)-1,3,4-thiadiazole, 2,5-bis(n-nonyldithio)-1,3,4-thiadiazole, 2,5-bis(1,1,3,3-tetramethylbutldithio)-1,3,4-thiadiazole, 2,5-bis(t-nonyl)-1,3,4-thiadiazole, 2,5-bis(t-nonylamino)-1,3,4-thiadiazole, 2,5-bis(t-nonylthio)-1,3,4-thiadiazole, 2,5-bis(t-nonyldithio)-1,3,4-thiadiazole, 2,5-bis(dimethylhexyl)-1,3,4-thiadiazole, 2,5-bis(dimethylhexylthio)-1,3,4-thiadiazole, 2,5-bis(dimethylhexylamino)-1,3,4-thiadiazole, 2,5-bis(dimethylhexyldithio)-1,3,4-thiadiazole, 2,5-bis(octadecenyl)-1,3,4-thiadiazole, 2,5-bis(octadecenylthio)-1,3,4-thiadiazole, 2,5-bis(octadecenylamino)-1,3,4-thiadiazole, 2,5-bis(octadecenyldithio)-1,3,4-thiadiazole, 2,5-bis(methylhexadecenyl)-1,3,4-thiadiazole, 2,5-bis(methylhexadecenylthio)-1,3,4-thiadiazole, 2,5-bis(methylhexadecenylamino)-1,3,4-thiadiazole, 2,5-bis(methylhexadecenyldithio)-1,3,4-thiadiazole, 2,5-bis(2-hydroxyoctadecyl)-1,3,4-thiadiazole, 2,5-bis(2-hydroxyoctadecylthio)-1,3,4-thiadiazole, 2,5-bis(2-hydroxyoctadecylamino)-1,3,4-thiadiazole, 2,5-bis(2-hydroxyoctadecyldithio)-1,3,4-thiadiazole, 2,5-bis(n-octoxycarbonylmethyl)-1,3,4-thiadiazole, 2,5-bis(n-octoxycarbonylmethylthio)-1,3,4-thiadiazole, 2,5-bis(n-octoxycarbonylmethylamino)-1,3,4-thiadiazole, 2,5-bis(n-octoxycarbonylmethyldithio)-1,3,4-thiadiazole, 2-mercapto-5-(2-ethylhexylthio)-1,3-4-thiadiazole, 2-mercapto-5-(2-ethylhexyldithio)-1,3-4-thiadiazole, 2-mercapto-5-(t-nonylthio)-1,3-4-thiadiazole, 2-mercapto-5-(t-nonyldithio)-1,3-4-thiadiazole, 2-amino-5-(2-ethylhexylamino)-1,3-4-thiadiazole, 2-amino-5-(t-nonylamino)-1,3-4-thiadiazole, 2-(2-ethylhexyl)-1,3,4-thiadiazole, 2-(t-nonyl)-1,3,4-thiadiazole, 3,5-bis(n-hexyldithio)-1,2,4-thiadiazole, 3,5-bis(n-octyldithio)-1,2,4-thiadiazole, 3,5-bis(n-nonyldithio)-1,2,4-thiadiazole, and 3,5-bis(1,1,3,3-tetramethylbutyldithio)-1,2,4-thiadiazole.

Examples of the polysulfide compound include a compound represented by the following general formula (2) (i.e., a dihydrocarbyl polysulfide).

R²¹—S_(x)—R²²  (2)

In the formula (2), R²¹ and R²² each independently represent a hydrocarbon group selected from an alkyl group having from 3 to 20 carbon atoms, an aryl group having from 6 to 20 carbon atoms, an alkylaryl group having from 7 to 20 carbon atoms, an arylalkyl group having from 7 to 20 carbon atoms, and an alkenyl group having from 3 to 20 carbon atoms, which may be the same as or different from each other; and x represents an integer of from 2 to 10. The alkyl group and the alkenyl group in R²¹ and R²² each may be linear or branched.

In the formula (2), R²¹ and R²² each preferably have from 6 to 18 carbon atoms, and x is preferably from 2 to 8, and more preferably from 3 to 7.

Specific examples of the dihydrocarbyl polysulfide include a dialkyl polysulfide, an olefin polysulfide, and a dibenzyl polysulfide.

Examples of the olefin polysulfide include a compound obtained by reacting an olefin having from 3 to 20 carbon atoms or a dimer to tetramer thereof with a sulfurizing agent, such as sulfur and a sulfur halide. Preferred examples of the olefin include propylene, isobutene, and diisobutene. Examples of the olefin polysulfide include a compound represented by the general formula (2), wherein one of R²¹ and R²² represents an alkenyl group, and the other thereof represents an alkenyl group or an alkyl group.

The sulfurized fat or fatty oil mean sulfurized product of animal or vegetable oil, and examples thereof include a sulfurized lard, a sulfurized canola oil, sulfurized castor oil, and sulfurized soybean oil. The sulfurized fat or fatty oil encompass a disulfurized fatty acid, such as sulfurized oleic acid, and a sulfurized ester, such as sulfurized methyl oleate.

The content of the non-metal-containing sulfur antioxidant (B) is not particularly limited within a range that does not impair the effects of the present invention, and in general, is preferably 0.1% by mass or more and 3.0% by mass or less, more preferably 0.3% by mass or more and 2.0% by mass or less, and further preferably 0.3% by mass or more and 1.5% by mass or less, based on the total amount of the lubricating oil composition.

<Hindered Amine Antioxidant (C) Having One Piperidine-Derived Skeleton in Molecule>

The lubricating oil composition of the present embodiment contains the hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule.

Examples of the piperidine-derived skeleton include a 2,2,6,6-tetramethylpiperidine skeleton, a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton.

In the following description, the “hindered amine antioxidant having one piperidine-derived skeleton in a molecule” may be referred to as a “monohindered amine antioxidant”.

The lubricating oil composition of the present embodiment has a content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition.

In the case where the content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom is less than 100 ppm by mass based on the total amount of the lubricating oil composition, the amount of a metal-based detergent necessary for increasing the total base number is increased, and thus the amount of deposits caused by the sulfated ash content due to the deterioration of the lubricating oil is increased to fail to suppress the wear of the engine components. In the case where the content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom exceeds 400 ppm by mass based on the total amount of the lubricating oil composition, the friction reducing capability after the deterioration of the lubricating oil composition cannot be retained. In particular, in the case where the lubricating oil composition contains a molybdenum friction modifier (E) described later, the excessive amount of the monohindered amine antioxidant (C) largely impairs the friction reducing capability based on the molybdenum friction modifier (E).

In the case where a hindered amine antioxidant having two piperidine-derived skeletons in a molecule (which may be hereinafter referred to as a “bishindered amine antioxidant”) and/or a hindered amine antioxidant having three or more piperidine-derived skeletons in a molecule is contained in an amount of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition, the amount of a metal-based detergent necessary for increasing the total base number can be decreased, but the friction reducing capability after the deterioration of the lubricating oil composition cannot be retained.

Consequently, for suppressing the wear of the engine components due to deposits caused by the sulfated ash content, and simultaneously retaining the friction reducing capability after the deterioration of the lubricating oil composition, it is necessary that the monohindered amine antioxidant (C) is used as the hindered amine antioxidant, and the content of the monohindered amine antioxidant is 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition.

The content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom is preferably 200 ppm by mass or more and 400 ppm by mass or less, more preferably 200 ppm by mass or more and 300 ppm by mass or less, and further preferably 200 ppm by mass or more and 250 ppm by mass or less, based on the total amount of the lubricating oil composition.

In the description herein, the content of nitrogen atom is a value that is measured according to JIS K2609:1998.

Specific examples of the monohindered amine antioxidant (C) include 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 2,2,6,6-tetramethylpiperidinyl methacrylate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, and 2,2,6,6-tetramethylpiperidin-4-yl dodecanoate.

The content of the monohindered amine antioxidant (C) is not particularly limited within a range that does not impair the effects of the present invention, and in general, is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.2% by mass or more and 0.9% by mass or less, and further preferably 0.4% by mass or more and 0.7% by mass or less, based on the total amount of the lubricating oil composition.

The lubricating oil composition of the present embodiment preferably does not substantially contain an amine antioxidant other than the monohindered amine antioxidant from the standpoint of the enhancement of the initial total base number and the standpoint of the retention of the friction reducing capability after the deterioration of the lubricating oil composition. In particular, the lubricating oil composition of the present embodiment preferably does not substantially contain a hindered amine antioxidant other than the monohindered amine antioxidant and/or a diarylamine antioxidant.

The expression “not substantially contain” herein means that the content of an amine antioxidant other than the monohindered amine antioxidant is less than 0.1% by mass, and preferably less than 0.01% by mass, based on the total amount of the lubricating oil composition.

<Metal-Based Detergent (D)>

The lubricating oil composition of the present embodiment preferably further contains a metal-based detergent (D). The metal-based detergent (D) contained in the lubricating oil composition may suppress the formation of deposits inside the engine, and may suppress the wear of the engine components.

The metal-based detergent (D) used may be, for example, one or more kind selected from a calcium-based detergent and a magnesium-based detergent, and one or more kind selected from a calcium-based detergent is preferably used from the standpoint of the fuel efficiency.

Examples of the calcium-based detergent include calcium sulfonate, calcium phenate, and calcium salicylate. Among these, calcium salicylate, which well suppresses the formation of deposits, is preferred.

Examples of the magnesium-based detergent include magnesium sulfonate, magnesium phenate, and magnesium salicylate. Among these, magnesium salicylate, which well suppresses the formation of deposits, is preferred.

The metal-based detergent preferably has a total base number of 150 mgKOH/g or more, more preferably from 150 to 500 mgKOH/g, further preferably from 150 to 450 mgKOH/g, and still further preferably from 180 to 400 mgKOH/g, from the standpoint of the detergency.

The content of the metal-based detergent (D) as converted in terms of metal atom is preferably 700 ppm by mass or more and 1,400 ppm by mass or less, more preferably 850 ppm by mass or more and 1,350 ppm by mass or less, and further preferably 1,000 ppm by mass or more and 1,250 ppm by mass or less, based on the total amount of the lubricating oil composition, from the standpoint of the enhancement of the total base number and the standpoint of the suppression of the sulfated ash content caused by the metal-based detergent (D).

In the description herein, the content of metal atom (for example, the content of metal atom based on the metal-based detergent (D)) and the content of molybdenum atom based on the molybdenum friction modifier (E)) is a value that is measured according to ASTM D4951.

The content of the metal-based detergent (D) is not particularly limited within a range that does not impair the effects of the present invention, and in general, is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 0.2% by mass or more and 5.0% by mass or less, and further preferably 0.5% by mass or more and 3.0% by mass or less, based on the total amount of the lubricating oil composition.

<Molybdenum Friction Modifier (E)>

The lubricating oil composition of the present embodiment preferably further contains a molybdenum friction modifier (E). The molybdenum friction modifier (E) contained in the lubricating oil composition may facilitate the improvement of the friction reducing capability of the lubricating oil composition.

The molybdenum friction modifier (E) used may be an organic compound having a molybdenum atom, and from the standpoint of the friction reduction, a molybdenum dithiophosphate (MoDTP) and a molybdenum dithiocarbamate (MoDTC) are preferred, and a molybdenum dithiocarbamate (MoDTC) is more preferred.

Examples of the molybdenum dithiocarbamate (MoDTC) include a compound represented by the following general formula (3).

In the formula (3), R³¹ to R³⁴ each independently represent a hydrocarbon group having from 5 to 18 carbon atoms, and may be the same as or different from each other. The number of carbon atoms of the hydrocarbon group is preferably from 5 to 16, more preferably from 8 to 14, and further preferably 12.

X³¹ to X³⁴ each independently represent an oxygen atom or a sulfur atom, and may be the same as or different from each other. The molar ratio of sulfur atom and oxygen atom (sulfur atom/oxygen atom) in X³¹ to X³⁴ is preferably from 1/3 to 3/1, and more preferably from 1.5/2.5 to 3/1, from the standpoint of the enhancement of the solubility thereon in the base oil (A).

Examples of the hydrocarbon group represented by R³¹ to R³⁴ include an alkyl group having from 5 to 18 carbon atoms, such as a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group; an alkenyl group having from 5 to 18 carbon atoms, such as an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, and a pentadecenyl group; a cycloalkyl group having from 5 to 18 carbon atoms, such as a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a methylcyclohexylmethyl group, a cyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group; an aryl group having from 6 to 18 carbon atoms, such as a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a terphenyl group; an alkylaryl group, such as a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, and a dimethylnaphthyl group; and an arylalkyl group having from 7 to 18 carbon atoms, such as a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.

The content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom is preferably 300 ppm by mass or more and 1,300 ppm by mass or less, more preferably 350 ppm by mass or more and 1,000 ppm by mass or less, and further preferably 400 ppm by mass or more and 800 ppm by mass or less, based on the total amount of the lubricating oil composition. In the case where the content thereof is 300 ppm by mass or more, the friction reducing capability of the lubricating oil composition can be improved, and in the case where the content thereof is 1,300 ppm by mass or less, the sulfated ash content can be decreased.

The content of the molybdenum friction modifier (E) is not particularly limited within a range that does not impair the effects of the present invention, and in general, is preferably 0.2% by mass or more and 2.0% by mass or less, more preferably 0.3% by mass or more and 1.5% by mass or less, and further preferably 0.5% by mass or more and 1.0% by mass or less, based on the total amount of the lubricating oil composition.

<Additives>

The lubricating oil composition of the present embodiment may contain additives, such as an ash-free detergent, an ash-free friction modifier, an anti-wear agent, an extreme pressure agent, a viscosity index improver, a metal deactivator, a pour point depressant, a rust inhibitor, and an anti-foaming agent, that do not correspond to the aforementioned components, in such a range that does not impair the effects of the present invention. The additives may be used alone or as a combination of two or more kinds thereof.

The contents of the additives each may be appropriately controlled within a range that does not impair the effects of the present invention, and each are generally from 0.001 to 15% by mass, preferably from 0.005 to 10% by mass, and more preferably from 0.01 to 8% by mass, based on the total amount of the lubricating oil composition.

The total content of the additives for a lubricating oil is preferably 25% by mass or less, more preferably 20% by mass or less, and further preferably 15% by mass or less, based on the total amount of the lubricating oil composition.

Examples of the ash-free detergent include an alkenylsuccinimide, such as an alkenylsuccinmonoimide and an alkenylsuccinbisimide, and a boron-modified alkenylsuccinimide.

Examples of the ash-free friction modifier include an aliphatic amine, an aliphatic ester, an aliphatic amide, a fatty acid, an aliphatic alcohol, and an aliphatic ether, each having at least one alkyl or alkenyl group having from 6 to 30 carbon atoms in a molecule.

Examples of the anti-wear agent and the extreme pressure agent include a sulfur-containing compound, such as zinc dithiophosphate; a phosphorus-containing compound, such as a phosphite ester compound, a phosphate ester compound, a phosphonate ester compound, and amine salts and metal salts of these compounds; and a sulfur and phosphorus-containing anti-wear agent, such as a thiophosphite ester compound, a thiophosphate ester compound, a thiophosphonate ester compound, and amine salts and metal salts of these compounds.

Examples of the viscosity index improver include a polymethacrylate, a dispersion type polymethacrylate, an olefin copolymer (such as an ethylene-propylene copolymer), a dispersion type olefin copolymer, and a styrene copolymer (such as a styrene-diene copolymer and a styrene-isoprene copolymer).

Examples of the corrosion inhibitor include a benzotriazole compound, a tolyltriazole compound, an imidazole compound, and a pyrimidine compound.

Examples of the pour point depressant include an ethylene-vinyl acetate copolymer, a condensate of chlorinated paraffin and naphthalene, a condensate of chlorinated paraffin and phenol, a polymethacrylate, and a polyalkylstyrene.

Examples of the rust inhibitor include a petroleum sulfonate, an alkylbenzene sulfonate, dinonylnaphthalene sulfonate, an alkenylsuccinate ester, and a polyhydric alcohol ester.

Examples of the anti-foaming agent include a silicone oil, a fluorosilicone oil, and a fluoroalkyl ether.

<Ratios of Components in Lubricating Oil Composition>

The lubricating oil composition of the present embodiment preferably has a ratio of the content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom and the content of the metal-based detergent (D) as converted in terms of metal atom [(content of monohindered amine antioxidant (C) as converted in terms of nitrogen atom)/(content of metal-based detergent (D) as converted in terms of metal atom)] of from 0.14 to 0.58, and more preferably from 0.15 to 0.30.

In the case where the ratio is 0.14 or more, the content of the metal-based detergent (D) can be suppressed to increase the total base number, and thereby the formation of deposits can be suppressed to suppress the wear of the engine components. In the case where the ratio is 0.58 or less, the content of the monohindered amine antioxidant (C) can be suppressed, and thereby the friction reducing capability after the deterioration of the lubricating oil composition can be readily retained, and the monohindered amine antioxidant (C) can be prevented from becoming deposits.

The lubricating oil composition of the present embodiment preferably has a ratio of the content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom and the content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom [(content of non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom)/(content of molybdenum friction modifier (E) as converted in terms of molybdenum atom)] of from 0.92 to 13.35, more preferably from 1.00 to 9.00, and further preferably from 2.00 to 9.00.

In the case where the ratio is 0.92 or more, the increase of the viscosity of the lubricating oil composition in the thermal deterioration thereof can be suppressed. In the case where the ratio is 13.35 or less, the friction reducing capability after the deterioration of the lubricating oil composition can be readily retained.

The lubricating oil composition of the present embodiment preferably has a ratio of the content of the monohindered amine antioxidant (C) as converted in terms of nitrogen atom and the content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom [(content of monohindered amine antioxidant (C) as converted in terms of nitrogen)/(content of molybdenum friction modifier (E) as converted in terms of molybdenum atom)] of from 0.15 to 1.35, more preferably from 0.20 to 0.60, and further preferably from 0.25 to 0.60.

In the case where the ratio is 0.15 or more, the friction reducing capability based on the molybdenum friction modifier (E) can be readily retained, after the deterioration of the lubricating oil composition. In the case where the ratio is 1.35 or less, a film of the molybdenum friction modifier (E) can be readily formed on the surface of the engine components.

<Sulfated Ash Content of Lubricating Oil Composition>

The lubricating oil composition of the present embodiment has a sulfated ash content of 0.70% by mass or less.

In the case where the sulfated ash content of the lubricating oil composition exceeds 0.70% by mass, the amount of deposits in the deterioration of the lubricating oil composition is increased, and the wear of the engine components cannot be suppressed.

The sulfated ash content of the lubricating oil composition is preferably 0.68% by mass or less, more preferably 0.67% by mass or less, and further preferably 0.66% by mass or less.

The lower limit of the sulfated ash content of the lubricating oil composition is not particularly limited, and is preferably 0.40% by mass or more, more preferably 0.45% by mass or more, and further preferably 0.50% by mass or more, from the standpoint of the increase of the total base number.

In the present embodiment, the sulfated ash content is a value that is measured according to JIS K2272:1998.

<Total Base Number of Lubricating Oil Composition>

The lubricating oil composition of the present embodiment has a total base number of 4.0 mgKOH/g or more.

In the case where the total base number of the lubricating oil composition is less than 4.0 mgKOH/g, the detergency of the lubricating oil composition becomes insufficient to facilitate the formation of deposits and to fail to suppress the wear of the engine components.

In the case where the total base number of the lubricating oil composition is too large, there may be a possibility of occurrence of the adverse effects in the case where the content of the monohindered amine antioxidant (C) is too large and the adverse effects in the case where the content of the metal-based detergent (D) is too large.

From these standpoints, the total base number of the lubricating oil composition is preferably from 4.0 to 7.0 mgKOH/g, more preferably from 4.2 to 7.0 mgKOH/g, and further preferably from 4.5 to 7.0 mgKOH/g.

In the present embodiment, the total base number is a value that is measured according to the hydrochloric acid method of JIS K2501:2003.

<Other Properties of Lubricating Oil Composition>

The lubricating oil composition of the present embodiment preferably has a content of sulfur atom of from 1,000 to 13,000 ppm by mass, more preferably from 2,000 to 11,000 ppm by mass, and further preferably from 2,000 to 9,000 ppm by mass, based on the total content of the lubricating oil composition.

In the case where the content of sulfur atom is 1,000 ppm by mass or more, the friction reducing capability after the deterioration of the lubricating oil composition can be retained, and in the case where the content thereof is 13,000 ppm by mass or less, the increase of the viscosity in the thermal deterioration of the lubricating oil composition can be suppressed.

The lubricating oil composition of the present embodiment preferably has a content of nitrogen atom of from 500 to 4,000 ppm by mass, more preferably from 700 to 3,500 ppm by mass, and further preferably from 900 to 3,000 ppm by mass, based on the total content of the lubricating oil composition.

In the case where the content of nitrogen atom is 500 ppm by mass or more, the detergency dispersibility can be improved, and in the case where the content thereof is 4,000 ppm by mass or less, the compatibility to a resin material, such as rubber, can be improved.

The lubricating oil composition of the present embodiment preferably has a kinematic viscosity at 100° C. of from 3 to 20 mm²/s, more preferably from 3 to 10 mm²/s, and further preferably from 5 to 8 mm²/s.

The lubricating oil composition of the present embodiment preferably has a viscosity index of 100 or more, more preferably 120 or more, and further preferably 130 or more.

<Application of Lubricating Oil Composition>

The lubricating oil composition of the present embodiment can be favorably used as a lubricating oil composition for an internal combustion engine, such as a gasoline engine, a diesel engine, and a gas engine, of an automobile, such as a four-wheel vehicle and a two-wheel vehicle, an electric power generator, a watercraft, and the like. In particular, the lubricating oil composition of the present embodiment can be favorably used as a lubricating oil composition for an engine equipped with a forced-induction mechanism, such as a supercharger and a turbocharger.

[Method for Producing Lubricating Oil Composition]

The method for producing a lubricating oil composition of the present embodiment includes preparing a lubricating oil composition containing a base oil (A), a non-metal-containing sulfur antioxidant (B), a hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule, and the preparing step is performed to satisfy the following conditions (i) to (iv).

-   -   (i) The lubricating oil composition has a content of the         non-metal-containing sulfur antioxidant (B) as converted in         terms of sulfur atom of 800 ppm by mass or more based on the         total amount of the lubricating oil composition.     -   (ii) The lubricating oil composition has a content of the         hindered amine antioxidant (C) as converted in terms of nitrogen         atom of 100 ppm by mass or more and 400 ppm by mass or less         based on the total amount of the lubricating oil composition.     -   (iii) The lubricating oil composition has a sulfated ash content         of 0.70% by mass or less.     -   (iv) The lubricating oil composition has a total base number of         4.0 mgKOH/g or more.

In the method for producing a lubricating oil composition of the present embodiment, the preferred embodiments of the constitutional components and the preferred embodiments of the numerical values of the conditions (i) to (iv) are the same as the preferred embodiments of the lubricating oil composition of the present embodiment described above.

EXAMPLES

The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples.

1. Measurement

The properties of the components constituting the lubricating oil compositions of Examples and Comparative Examples and the properties of the lubricating oil compositions of Examples and Comparative Examples were measured according to the following methods.

<Sulfated Ash Content>

The sulfated ash content was measured according to JIS K2272:1998.

<Total Base Number>

The total base number was measured according to the hydrochloric acid method of JIS K2501:2003.

<Content of Sulfur Atom>

The content of sulfur atom was measured according to ASTM D-1552.

<Content of Nitrogen Atom>

The content of nitrogen atom was measured according to JIS K2609:1998.

<Content of Metal Atom>

The content of metal atom was measured according to ASTM D4951.

<Kinematic Viscosity at 100° C.>

The kinematic viscosity was measured according to JIS K2283:2000.

<Viscosity Index>

The viscosity index was measured according to JIS K2283:2000.

2. Preparation of Lubricating Oil Composition

The lubricating oil compositions of Examples and Comparative Examples were prepared according to the compositional ratios shown in Tables 1 and 2. The details of the base oils and the additives used in Examples and Comparative Examples are shown below.

<Base Oil (A)>

Mineral oil of 100 N, sulfur content: 10 ppm or less, kinematic viscosity at 100° C.: 4.2 mm²/s, viscosity index: 126

<Non-Metal-Containing Sulfur Antioxidant>

B-1: Thiocarbamate compound corresponding to general formula (1A) (Vanlube 7723, produced by R.T. Vanderbilt Company, Inc., sulfur content: 30.5% by mass, nitrogen content: 6.9% by mass)

B-2: Thiadiazole compound (HiTEC 4313, produced by Afton Chemical Corporation, sulfur content: 36.0% by mass, nitrogen content: 5.7% by mass)

B-3: Polysulfide compound (Dailube GS-120, a trade name, produced by DIC Corporation, sulfur content: 11.4% by mass)

B-4: Sulfurized fat or fatty oil (Dailube GS-440L, a trade name, produced by DIC Corporation, sulfur content: 39.7% by mass)

<Amine Antioxidant>

Monohindered amine antioxidant (XPDL590, a trade name, produced by BASF AG, nitrogen content: 4.3% by mass)

Bishindered amine antioxidant 1 (Tinuvin 765, a trade name, produced by BASF AG, nitrogen content: 5.3% by mass, number of piperidine-derives skeletons in molecule: 2)

Bishindered amine antioxidant 2 (Tinuvin 770DF, a trade name, produced by BASF AG, nitrogen content: 5.6% by mass, number of piperidine-derives skeletons in molecule: 2)

Diarylamine antioxidant (diphenylamine, Irganox L57, a trade name, produced by BASF AG, nitrogen content: 4.6% by mass)

<Metal-Based Detergent (D)>

Calcium salicylate (total base number: 225 mgKOH/g, calcium atom content: 7.8% by mass)

<Molybdenum Friction Modifier (E)>

Molybdenum dithiocarbamate (Sakura-Lube 515, a trade name, produced by Adeka Corporation, molybdenum atom content: 10.0% by mass)

<Additive Mixture>

Additive mixture containing a viscosity index improver, a pour point depressant, polybutenylsuccinimide, boron-modified polybutenylsuccinimide, zinc dialkyldithiophosphate, a rust inhibitor, a corrosion inhibitor, and a anti-foaming agent

3. Evaluation

The lubricating oil compositions of Examples and Comparative Examples were measured for the friction coefficient after a deterioration treatment. The results are shown in Tables 1 and 2.

<Friction Coefficient after Deterioration Treatment>

To 100 g of each of the lubricating oil compositions of Examples and Comparative Examples immediately after the production, 0.5% by mass of 4-ethylnitrobenzene as a deterioration accelerator was added. Furthermore, the lubricating oil composition was subjected to a deterioration treatment by blowing a gas having a NO_(x) concentration of 2,000 ppm by volume therein for 48 hours at an oil temperature of 160° C. The deterioration treatment corresponds to the deterioration occurring by driving an automobile for approximately 10,000 km.

The lubricating oil composition after the deterioration treatment was subjected to a preconditioning operation under the following condition for 2 hours and then measured for the friction coefficient with the testing machine shown below.

Testing machine: MTM (mini traction machine) tester, produced by PCS Instruments, Ltd.

Test piece: Standard test piece (¾″ steel-steel)

Condition for preconditioning operation and measurement of friction coefficient: oil temperature: 80° C., load: 30 N, velocity: 100 mm/s, specific sliding ratio (SSR): 50%, oil amount: 35 mL

TABLE 1 Example 1 2 3 Composition Base oil (A) balance balance balance (% by mass) Non-metal containing sulfur antioxidant (B) B-1 0.50 1.00 2.00 B-2 — — — B-3 — — — B-4 — — — Amine antioxidant Monohindered amine antioxidant (C) 0.50 0.50 0.50 Bishindered amine antioxidant 1 — — — Bishindered amine antioxidant 2 — — — Diphenylamine — — — Metal-based detergent (D) 1.50 1.50 1.50 Molybdenum friction modifier (E) 0.70 0.70 0.70 Additive mixture 15.00 15.00 15.00 Contents and content Sulfur atom content derived from component (B) (ppm by mass) [i] 1525 3050 6100 ratios of component Nitrogen atom content derived from amine antioxidant (ppm by mass) [ii] 215 215 215 Metal atom content derived from component (D) (ppm by mass) [iii] 1170 1170 1170 Molybdenum atom content derived from component (E) (ppm by mass) [iv] 700 700 700 [ii]/[iii] 0.18 0.18 0.18 [i]/[iv] 2.18 4.36 8.71 [ii]/[iv] 0.31 0.31 0.31 Contents of atoms Calcium atom content (ppm by mass) 1240 1280 1280 based on total amount of Sulfur atom content (ppm by mass) 3500 5200 8000 composition Nitrogen atom content (ppm by mass) 1400 1800 2400 Properties Total base number (mgKOH/g) 4.69 4.65 4.65 Sulfated ash content (% by mass) 0.63 0.65 0.65 Evaluation Friction coefficient after deterioration 0.0798 0.0589 0.041 Total base number after deterioration (mgKOH/g) 1.28 1.48 1.52 Example 4 5 6 Composition Base oil (A) balance balance balance (% by mass) Non-metal containing sulfur antioxidant (B) B-1 — — — B-2 0.42 — — B-3 — 1.34 — B-4 — — 0.38 Amine antioxidant Monohindered amine antioxidant (C) 0.50 0.50 0.50 Bishindered amine antioxidant 1 — — — Bishindered amine antioxidant 2 — — — Diphenylamine — — — Metal-based detergent (D) 1.50 1.50 1.50 Molybdenum friction modifier (E) 0.70 0.70 0.70 Additive mixture 15.00 15.00 15.00 Contents and content Sulfur atom content derived from component (B) (ppm by mass) [i] 1512 1528 1509 ratios of component Nitrogen atom content derived from amine antioxidant (ppm by mass) [ii] 215 215 215 Metal atom content derived from component (D) (ppm by mass) [iii] 1170 1170 1170 Molybdenum atom content derived from component (E) (ppm by mass) [iv] 700 700 700 [ii]/[iii] 0.18 0.18 0.18 [i]/[iv] 2.16 2.18 2.16 [ii]/[iv] 0.31 0.31 0.31 Contents of atoms Calcium atom content (ppm by mass) 1280 1280 1280 based on total amount of Sulfur atom content (ppm by mass) 3500 3600 3500 composition Nitrogen atom content (ppm by mass) 1400 1100 1100 Properties Total base number (mgKOH/g) 4.92 4.70 4.71 Sulfated ash content (% by mass) 0.65 0.65 0.65 Evaluation Friction coefficient after deterioration 0.0812 0.0805 0.0686 Total base number after deterioration (mgKOH/g) 1.28 1.05 1.03

TABLE 2 Comparative Example 1 2 3 4 Composition Base oil (A) balance balance balance balance (% by mass) Non-metal containing B-1 — — 0.25 0.50 sulfur antioxidant (B) B-2 — — — — B-3 — — — — B-4 — — — — Amine antioxidant Monohindered amine antioxidant — — 0.50 1.00 (C) Bishindered amine antioxidant 1 — — — — Bishindered amine antioxidant 2 — — — — Diphenylamine — — — — Metal-based detergent (D) 1.50 2.00 1.50 1.50 Molybdenum friction modifier (E) 0.70 0.70 0.70 0.70 Additive mixture 15.00 15.00 15.00 15.00 Contents and content Sulfur atom content derived from component (B) (ppm by — — 763 1525 ratios of component mass) [i] Nitrogen atom content derived from amine antioxidant (ppm — — 215 430 by mass) [ii] Metal atom content derived from component (D) (ppm by 1170 1560 1170 1170 mass) [iii] Molybdenum atom content derived from component (E) (ppm 700 700 700 700 by mass) [iv] [ii]/[iii] — — 0.18 0.37 [i]/[iv] — — 1.09 2.18 [ii]/[iv] — — 0.31 0.61 Contents of atoms Calcium atom content (ppm by mass) 1260 1700 1260 1240 based on total amount of Sulfur atom content (ppm by mass) 2200 2200 2800 3600 composition Nitrogen atom content (ppm by mass) 900 900 1300 1600 Properties Total base number (mgKOH/g) 3.90 4.96 4.71 5.48 Sulfated ash content (% by mass) 0.64 0.78 0.64 0.63 Evaluation Friction coefficient after deterioration 0.1041 0.1058 0.1203 0.1050 Total base number after deterioration (mgKOH/g) 0.25 0.90 1.21 2.09 Comparative Example 5 6 7 Composition Base oil (A) balance balance balance (% by mass) Non-metal containing sulfur B-1 0.50 0.50 0.50 antioxidant (B) B-2 — — — B-3 — — — B-4 — — — Amine antioxidant Monohindered amine antioxidant — — — (C) Bishindered amine antioxidant 1 0.41 — — Bishindered amine antioxidant 2 — 0.39 — Diphenylamine — — 0.47 Metal-based detergent (D) 1.50 1.50 1.50 Molybdenum friction modifier (E) 0.70 0.70 0.70 Additive mixture 15.00 15.00 15.00 Contents and content Sulfur atom content derived from component (B) (ppm 1525 1525 1525 ratios of component by mass) [i] Nitrogen atom content derived from amine antioxidant (ppm 217 217 217 by mass) [ii] Metal atom content derived from component (D) (ppm by 1170 1170 1170 mass) [iii] Molybdenum atom content derived from component (E) (ppm 700 700 700 by mass) [iv] [ii]/[iii] 0.19 0.19 0.19 [i]/[iv] 2.18 2.18 2.18 [ii]/[iv] 0.31 0.31 0.31 Contents of atoms Calcium atom content (ppm by mass) 1280 1270 1270 based on total amount of Sulfur atom content (ppm by mass) 3500 3400 3400 composition Nitrogen atom content (ppm by mass) 1400 1500 1400 Properties Total base number (mgKOH/g) 4.72 4.79 3.84 Sulfated ash content (% by mass) 0.65 0.65 0.65 Evaluation Friction coefficient after deterioration 0.1149 0.1148 0.0628 Total base number after deterioration (mgKOH/g) 1.44 1.46 1.13

It can be confirmed from Tables 1 and 2 that the lubricating oil compositions of Examples 1 to 6 can retain the good friction reducing capability even after the deterioration thereof. The lubricating oil compositions of Examples 1 to 6 each have a total base number of 4.0 mgKOH/g or more irrespective of the small sulfated ash content of 0.70% by mass or less, and thus are expected to achieve good detergency. The lubricating oil compositions of Examples 1 to 6 each have a small sulfated ash content of 0.70% by mass or less, and thus are expected to suppress the wear of the engine components due to deposits. The lubricating oil composition of Examples 1 to 6 each have a total base number of 1.0 mgKOH/g or more after the deterioration thereof, and thus are expected to achieve the detergency for a prolonged period of time.

On the other hand, it can be confirmed that the lubricating oil compositions of Comparative Examples 1 to 6 cannot retain the good friction reducing capability after the deterioration thereof. The lubricating oil compositions of Comparative Examples 1 and 7 each have a total base number of less than 4.0 mgKOH/g, and therefore the lubricating oil compositions are insufficient in detergency, tend to form deposits, and cannot be expected to suppress the wear of the engine components. The lubricating oil composition of Comparative Example 2 has a sulfated ash content exceeding 0.70% by mass, and thus cannot be expected to suppress the wear of the engine components due to deposits. The lubricating oil compositions of Comparative Examples 1 and 2 each have a total base number of less than 1.0 mgKOH/g after the deterioration thereof, and thus cannot be expected to achieve the detergency for a prolonged period of time. 

1. A lubricating oil composition, comprising: (A) a base oil (A); (B) a non-metal-containing sulfur antioxidant (B); and (C) a hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule, wherein: a content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom of 800 ppm by mass or more based on the total amount of the lubricating oil composition; a content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition; a sulfated ash content of 0.70% by mass or less; and a total base number of 4.0 mgKOH/g or more.
 2. The lubricating oil composition according to claim 1, wherein the non-metal-containing sulfur antioxidant (B) is at least one selected from the group consisting of a thiocarbamate compound, a thiadiazole compound, a polysulfide compound, and a sulfurized fat or fatty oil.
 3. The lubricating oil composition according to claim 1, wherein the content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom is 1,200 ppm by mass or more and 6,500 ppm by mass or less based on the total amount of the lubricating oil composition.
 4. The lubricating oil composition according to claim 1, wherein the content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom is 200 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition.
 5. The lubricating oil composition according to claim 1, further comprising: (D) a metal-based detergent (D), wherein a content of the metal-based detergent (D) as converted in terms of metal atom of 700 ppm by mass or more and 1,400 ppm by mass or less based on the total amount of the lubricating oil composition.
 6. The lubricating oil composition according to claim 5, wherein the ratio of the content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom and the content of the metal-based detergent (D) as converted in terms of metal atom [(content of hindered amine antioxidant (C) as converted in terms of nitrogen atom)/(content of metal-based detergent (D) as converted in terms of metal atom)] is from 0.14 to 0.58.
 7. The lubricating oil composition according to claim 1, further comprising: (E) a molybdenum friction modifier (E), wherein a content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom of 300 ppm by mass or more and 1,300 ppm by mass or less based on the total amount of the lubricating oil composition.
 8. The lubricating oil composition according to claim 7, wherein the ratio of the content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom and the content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom [(content of non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom)/(content of molybdenum friction modifier (E) as converted in terms of molybdenum atom)] is from 0.92 to 13.35.
 9. The lubricating oil composition according to claim 7, wherein the ratio of the content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom and the content of the molybdenum friction modifier (E) as converted in terms of molybdenum atom [(content of hindered amine antioxidant (C) as converted in terms of nitrogen)/(content of molybdenum friction modifier (E) as converted in terms of molybdenum atom)] is from 0.15 to 1.35.
 10. The lubricating oil composition according to claim 1, wherein the content of the base oil (A) is less than 90% by mass based on the total amount of the lubricating oil composition.
 11. A lubricating oil composition for an engine equipped with a forced-induction mechanism, the composition comprising the lubricating oil composition of claim
 1. 12. A method for producing a lubricating oil composition, the method comprising preparing a lubricating oil composition containing a base oil (A), a non-metal-containing sulfur antioxidant (B), a hindered amine antioxidant (C) having one piperidine-derived skeleton in a molecule, the preparing step being performed to satisfy the following conditions (i) to (iv): (i) the lubricating oil composition having a content of the non-metal-containing sulfur antioxidant (B) as converted in terms of sulfur atom of 800 ppm by mass or more based on the total amount of the lubricating oil composition, (ii) the lubricating oil composition having a content of the hindered amine antioxidant (C) as converted in terms of nitrogen atom of 100 ppm by mass or more and 400 ppm by mass or less based on the total amount of the lubricating oil composition, (iii) the lubricating oil composition having a sulfated ash content of 0.70% by mass or less, and (iv) the lubricating oil composition having a total base number of 4.0 mgKOH/g or more. 